Although it is now relatively well established that mammalian cells (including human cells) repair DNA damage produced by chemical carcinogens, relatively little is known about the details of DNA repair mechanisms or about the biological consequences of repair. The proposed project will utilize methodology developed by us to look at the removal of bound carcinogen (e.g. N-acetoxy-2-acetylaminofluorene) under conditions of relatively high cell survival from normal human cells, Xeroderma pigmentosum cells (complementation groups A-E and variants), and cells from other individuals at high risk for cancer (Fanconi's anemia, ataxia telangiectasia, Bloom's syndrome). The major aim of this aspect of our work will be to resolve discrepancies in the literature concerning the repair competence of these cells and to identify a series of "mutant" human cell strains with varying competence to remove bound carcinogen. In addition to these quantitative studies, analysis of the distribution of repair within the human genome will be continued. Our previous studies have indicated that repair is not randomly distributed throughout the genome, but the basis of this selectivity has eluded us. Recent analysis of chromatin structure has indicated that DNA may be fractionated into histone associated complexes ("nu bodies," nucleosomes) and linker regions. We will take advantage of this and related technology to determine if this aspect of chromatin structure is the basis for the selectivity of repair processes and if mutants with partial repair competence repair certain regions of chromatin preferentially. In order to gain understanding of the functional implications of carcinogen damage and repair, analysis of RNA transcription (hnRNA) and processing (mRNA production, poly A addition, 5' capping, and protein complexing) will be carried out in normal cells, partially repair-competent cells and repair-incompetent cells after treatment with carcinogen.